Using raise in GCD can cause timing issues with the signal mechanism.

when we use raise in GCD, the signal handler is executed asynchronously, whereas in pthread, it is executed synchronously as expected.

example:

#include <Foundation/Foundation.h>
#include <pthread/pthread.h>

static void HandleSignal(int sigNum, siginfo_t* signalInfo, void* userContext) {
    printf("handle signal %d\n", sigNum);
    printf("begin sleep\n");
    sleep(3);
    printf("end sleep\n");
}

void InstallSignal(void) {
    static const int g_fatalSignals[] =
    {
        SIGABRT,
        SIGBUS,
        SIGFPE,
        SIGILL,
        SIGPIPE,
        SIGSEGV,
        SIGSYS,
        SIGTRAP,
    };
    int fatalSignalsCount = sizeof(g_fatalSignals) / sizeof(int);
    struct sigaction action = {{0}};
    action.sa_flags = SA_SIGINFO | SA_ONSTACK;
#if defined(__LP64__)
    action.sa_flags |= SA_64REGSET;
#endif
    sigemptyset(&action.sa_mask);
    action.sa_sigaction = &HandleSignal;
    struct sigaction pre_sa;
    for(int i = 0; i < fatalSignalsCount; i++) {
        int sigResult = sigaction(g_fatalSignals[i], &action, &pre_sa);
    }
}

void* RaiseAbort(void *userdata) {
    raise(SIGABRT);
    printf("signal handler has finished\n");
    return NULL;
}

int main(int argc, const char * argv[]) {

    InstallSignal();

    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        raise(SIGABRT);
        // abort(); // abort() is ok
        RaiseAbort(nullptr);
    });
    
    // pthread is ok
    // pthread_t tid;
    // int ret = pthread_create(&tid, NULL, RaiseAbort, NULL);
    // if (ret != 0) {
    //     fprintf(stderr, "create thread failed\n");
    //     return EXIT_FAILURE;
    // }
    [[NSRunLoop mainRunLoop] run];
    return 0;
}

console log:

signal handler has finished
handle signal 6
begin sleep
end sleep